It is well documented that Interstitial Cell Stimulating Hormone (ICSH) and Follicle Stimulating Hormone (FSH) will promote the synthesis of testosterone by the testis. When ICSH and FSH are used in combination a synergistic response is noted (augmented testosterone production). This project will study augmented steroid production by rabbit testis slices stimulated by ICSH, FSH and ICSH/FSH combinations in vitro. The end point for these studies will be testosterone production by testis slices. Testosterone will be quantitated by radioimmunoassay techniques after a preliminary purification by celite column chromatography in which propylene glycol is the stationary phase and a graded series of iso-octane-benzene solvent mixtures are the mobile phases. Testosterone is adequately separated from dihydrotestosterone by this column. This separation allows a specific estimate of testosterone production. In some cases, isotopic precursor incorporation into the various intermediates which occur in the biosynthetic pathway leading to the formation of testosterone will be determined. Analytical methods utilized in these studies will include paper chromatography, thin-layer chromatography, various chemical derivative formations, recrystallization techniques, and liquid scintillation spectrometry. Studies are planned to determine the specific activity of some of the steroid biosynthetic intermediates, and this would involve gas chromatography.